Is it permissible for my father to sell land he does not yet own, knowing its boundaries but not its exact location, given that the buyer (his friend) has agreed to the purchase and paid the full price?

It is permissible to sell an undivided share of land if its boundaries and area are known, and the proportion of the undivided share is specified, whereby the buyer becomes a co-owner with the remaining owners. The jurists have reached a consensus on the permissibility of this.

It is necessary to inform the co-owners before the sale, based on what Muslim narrated from Jabir, that the Messenger of Allah, peace and blessings be upon him, ruled with pre-emption in every partnership that has not been divided. If he does not inform them, he has acted wrongly, and they have the right of pre-emption.